This invention relates to an apparatus for treating waste water and in particular to an apparatus for removing fats, oils and grease (hereinafter referred to as FOG) from waste water downstream of a washing facility, such as a sink in a commercial kitchen.
Typically, waste water drained from a sink in a commercial kitchen or catering facility contains grease in an emulsified state, as well as grease laden solids in suspension, typically in the form of foods wastes. Such contaminants can cause blockages in drainage systems and/or fouling of filtration systems or pumps within water treatment plants downstream of the drainage system.
Effluent from FOG contamination points in commercial kitchens typically originates from steam combination ovens, convection rotisserie ovens, pot sinks, pre-rinse sinks, dishwashers, canopies, and the like. They have in common the use and application of hot water ranging in temperature from 40° C. to 85° C. for the purposes of dealing with FOG contamination, where FOG is washed away in the waste water stream from such devices.
For these reasons, depending on the country, it is often compulsory for commercial kitchen operations to fit some kind of interceptor device to collect the FOG before it enters the sewer, typically referred to as a grease trap. Additionally, where FOG is a concern in the local wastewater collection system, inspection programs have been set up to ensure that these grease traps and/or interceptors are being maintained on a routine basis.
Known grease traps range in complexity from simple settling tanks, known as “passive” grease traps, that require periodic manual grease removal, to rather complex structural arrangements that provide for automatic skimming and collection of skimmed fats, oils and grease into external containers positioned adjacent the trap assembly, commonly referred to as “automated” grease traps.
Passive grease traps are, in essence, simply a settling tank having a wastewater inlet at one end and an outlet at an opposite end for connection to a drain. Often baffle plates are arranged within the tank to interrupt direct flow-through of wastewater between the inlet and the outlet. Periodically, an employee must manually skim the FOG that has accumulated at the surface of the wastewater. This is an extremely unpleasant and time-consuming task.
Automated grease traps include automatic skimmer arrangements, typically utilizing a rotating skimmer device, in the form of a disc, drum, endless belt or tube, mounted above the tank and connected to a drive arrangement to move the skimming device into and out of the waste water within the tank of the grease trap. The skimming device collects FOG from the surface of the water in the tank as it moves out of the water and is subsequently cleaned by means providing a scraping or squeezing action on the skimming device, such as wiper blades, arranged to direct the collected FOG into a collection device before the skimming device passes back into the water. The collection device is typically a separate container or reservoir located on one side of the tank.
Known grease traps require a regular maintenance program to be carried out to pump out such traps and refill with clean water. The European Standard EN 1825 calls for grease traps to be pumped monthly and preferentially fortnightly. In so far as grease traps contain some if not all of the entrained FOG and food wastes, these separate, with FOG having a specific gravity of less than 1 rising to the surface and food waste having a specific gravity greater than 1 sinking to the bottom.
Saturated fats, and animal fats in particular, are viscous above 40° C. but may be prone to solidify below such temperature. They are emulsified in the hot water. Hot water is used to remove FOG and to leave crockery, cutlery and pots and pans free and clear of FOG. Most known automated grease traps are only effective when the temperature of the waste water in the grease trap is around 40° C. to ensure that the FOG, in particular the more waxy components thereof, remain in viscous form and do not form a solid crust on top of the waste water. Therefore, known automated grease traps typically incorporate electrical heating elements within the grease trap. Such heating elements consume considerable electrical power and can cause a fire risk if overheating occurs or if the heating elements become exposed to the air.
Furthermore, at such temperatures the mesophilic range of aerobic bacteria quickly consume the available oxygen dissolved in the waste water as they seek to metabolize the organic matter. Conditions turn anaerobic and foul smells occur. The malodour issues associated with grease traps is evident whether you walk along a street in a tourist area with FSEs in abundance on a nice summer's night and smell the malodours wafting up from the sewers or open a conventional grease trap to be assaulted by noxious odours.
A further issue is that grease traps tend not to be regularly maintained, thus further contributing to the inefficiency of grease traps. The evidence in support of such a statement is the raft of statistics available from the drainage network companies as to the number of blockages attributable to FOG and to the service providers who clear drain blockages. The number of blockages and pollution incidents relating to fat, oil and grease are also increasing. There are approximately 200,000 sewer blockages throughout the UK every year of which up to 75% are caused by FOG. Clearing these blockages costs millions of pounds a year. Businesses also risk blocking their own drainage systems, which results in extra costs being incurred in clean-up efforts. These fat blockages can result in sewer flooding, odour problems and the risk of rat infestations, both near and beyond the affected premises. In fact, every outlet disposing of fat, oil and grease into sinks and drains is at risk of experiencing damaging and costly drainage problems. In the United States, each year sewers back up annually an estimated 400,000 times, and municipal sewer overflows on 40,000 occasions. The EPA has determined that sewer pipe blockages are the leading cause of sewer overflows, and grease is the primary cause of sewer blockages. Even if accumulated FOG does not escalate into blockages and sanitary sewer overflows, it can disrupt wastewater utility operations and increase operations and maintenance requirements.